Under the crane's working conditions, a Wound Rotor Line-start Permanent Magnet Synchronous Motor (WRLSPMSM) is designed in this paper. Rotor external resistance can be connected to the prototype, and rotor resistance determines when the maximum torque appears. So this paper puts forward a method to improve the starting performance, which PWM chopping is adopted to control rotor external DC fixed resistance. Because the number of rotor external AC resistance is limited, the starting torque has fluctuation when rotor external AC resistance is switched. Rotor external DC fixed resistance is controlled by PWM chopper technology. Regulate the rotor external DC fixed resistance rapidly to reduce torque ripple and realize speed stepless. Detailed theoretical analysis shows that starting torque is mainly affected by asynchronous torque and generated braking torque, and also according the analysis determines the value of rotor external DC fixed resistance. Meanwhile considering the influence of slots per pole per phase q on cogging torque, which easily disturbs the system's precise controlling during the low speed running, the fraction-slot winding is adopted in the prototype. The PWM chopping control method makes the starting process safer and more convenient than asynchronous motor.
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